Cambrian

The Cambrian is the first geological period of the Paleozoic Era and the Phanerozoic Eon. It lasted about 51.95 million years, from 538.8 million years ago to 486.85 million years ago.

During this time, most of the continents were gathered in the southern hemisphere, surrounded by a huge ocean called the Panthalassa Ocean. One of these continents, Gondwana, began to form and changed the Earth's climate and landscapes.

The Cambrian is very important for what happened to life on our planet. Before this period, most living things were very simple, single-celled organisms. But during the Cambrian, something amazing occurred called the Cambrian explosion. Many new, more complex animals with different body plans appeared quickly. This was the first time we see representatives of most major animal groups that exist today. The Cambrian also has many special fossil sites, called lagerstätte, where scientists can find extremely well-preserved remains, showing even soft parts of ancient animals.

Etymology and history

The word Cambrian comes from the Latin name for Wales, Cambria, where scientists first studied rocks from this time. The name was created by a scientist named Adam Sedgwick in 1831 after his work in North Wales. He split the Cambrian into three parts: Lower, Middle, and Upper.

Sedgwick and another scientist, Roderick Murchison, worked together to define the end of the Cambrian period. However, they disagreed about where the boundary should be. It wasn't until 1879 that another scientist, Charles Lapworth, solved the problem by naming the disputed rocks the Ordovician period. The name Cambrian was officially accepted in 1960.

Geology

Systems, series and stages can be defined globally or regionally. For global stratigraphic correlation, the ICS ratify rock units based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) identifying the lower boundary of the unit. Currently the boundaries of the Cambrian System, three series and six stages are defined by global stratotype sections and points.

The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier, has led to calls for a more precisely defined base to the Cambrian Period.

The Terreneuvian is the lowermost series/epoch of the Cambrian, lasting from 538.8 ± 0.6 Ma to c. 521 Ma. It is divided into two stages: the Fortunian stage, 538.8 ± 0.6 Ma to c. 529 Ma; and the unnamed Stage 2, c. 529 Ma to c. 521 Ma. The name Terreneuvian was ratified by the International Union of Geological Sciences (IUGS) in 2007, replacing the previous "Cambrian Series 1". The Terreneuvian is the only series in the Cambrian to contain no trilobite fossils.

The Miaolingian is the third series/epoch of the Cambrian, lasting from c. 506.5 Ma to c. 497 Ma. It is divided into three stages: the Wuliuan c. 506.5 Ma to 504.5 Ma; the Drumian c. 504.5 Ma to c. 500.5 Ma; and the Guzhangian c. 500.5 Ma to c. 497 Ma.

The Furongian, c. 497 Ma to 486.85 ± 1.5 Ma, is the fourth and uppermost series/epoch of the Cambrian. The Furongian is divided into three stages: the Paibian, c. 497 Ma to c. 494 Ma, and the Jiangshanian c. 494.2 Ma to c. 491 Ma, which have defined GSSPs; and the unnamed Cambrian Stage 10, c. 491 Ma to 486.85 ± 1.5 Ma.

Major meteorite impact structures include: the early Cambrian (c. 535 Ma) Neugrund crater in the Gulf of Finland, Estonia; the 5 km diameter Gardnos crater (500±10 Ma) in Buskerud, Norway; the 24 km diameter Presqu'ile crater (500 Ma or younger) Quebec, Canada; the 19 km diameter Glikson crater (c. 508 Ma) in Western Australia; the 5 km diameter Mizarai crater (500±10 Ma) in Lithuania; and the 3.2 km diameter Newporte structure (c. 500 Ma or slightly younger) in North Dakota, U.S.A.

Paleogeography

During the Cambrian period, the positions of continents were determined using clues from rocks and fossils. Scientists use these clues to understand how Earth looked long ago, but there is still some debate about exactly where each landmass was.

Most models show that a large landmass called Gondwana stretched from near the South Pole up towards the equator. Another large landmass, Laurentia, sat near the equator, separated from Gondwana by a wide ocean called the Iapetus Ocean. Smaller continents such as Baltica, Siberia, and parts of China drifted in different directions, shaping the early oceans and seas of our planet.

Climate

The Cambrian period had a warm, greenhouse climate with high levels of carbon dioxide in the air. This warmth affected the whole planet, from the poles to the equator. Scientists think average temperatures were around 20–25 °C (68–77 °F), much warmer than today.

The oceans were also warm, and oxygen levels in the air were lower than they are now, between 3% and 14% of today’s levels. These warm, low-oxygen conditions influenced the kinds of animals that could live in the seas and helped shape life on Earth during this ancient time.

Geochemistry

During the Cambrian, the chemistry of the oceans and atmosphere changed often. These changes are shown in the ratios of different elements found in rocks. These changes happened because of many factors, including volcanic activity, weather patterns, and the actions of early sea creatures.

The start of the Cambrian saw a big change in carbon ratios, showing low oxygen levels in shallow seas. This was when many new animal groups began to appear. Later in the Cambrian, more changes happened as mountains eroded and volcanoes erupted, affecting the oceans and the creatures living there. These changes led to more oxygen in some areas and less in others, influencing which animals could survive and thrive. The chemistry of the seas also affected the kinds of shells and skeletons that animals could build.

Flora

The Cambrian period had simple plants, mostly in the ocean. Important sea plants included Fuxianospira, Sinocylindra, and Marpolia. There were no known plants on land during this time.

Although scientists think land plants might have started to appear in the late Cambrian, the first clear evidence of land plants comes from the following period, the Ordovician. Microbes formed mats on beaches and helped shape early soils.

Oceanic life

The Cambrian explosion was a time when many new animals quickly appeared and grew. Most of these animals lived in the ocean. Although trilobites seemed very common because of their strong, rocky shells, they were actually just a small part of all the ocean animals. Other animals with softer bodies were more common but harder to find as fossils.

During this period, the variety of life in the sea changed a lot. Many older sea creatures disappeared, and new types of animals began to dig into the ocean floor. This digging changed the sea floor forever. Even though life was booming at first, later in the Cambrian period, the number of animal species actually went down because of changes in the ocean’s oxygen and chemical levels. Some sea life even began to move onto land, leaving behind tracks in the mud as evidence of their journey.

Symbol

The United States Federal Geographic Data Committee uses a special symbol, a "barred capital C" ⟨Ꞓ⟩, to represent the Cambrian Period. This symbol is part of Unicode, which is a system that includes characters from many writing systems around the world. The specific code for this symbol is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.